hi, do as you see fit.
follow johnny5, since he know's all.
including whats behind my dash & whats connected to my ECU's tundra.
thats why his speedo is off & mine is dead on.
he knows everything.
yes, he is correct about the diameter.
if you had 31" tall rim & tire combo & no matter what combo you put on, if it still was 31"s.
you don't need to do anything.
gorilla